A Planar π-Conjugated Naphthyridine-Based N-Heterocyclic Carbene Ligand and Its Derived Transition-Metal Complexes

Abstract

HL·(PF6) (L = 2,4-dimethyl-8-phenyl[1,2,4]triazolo[4,3-a][1,8]naphthyridin-9-ylidene) was synthesized from the nucleophilic reaction of 7-chloro-2,4-dimethyl-1,8-naphthyridine with phenylhydrazine and subsequent acidification, anion exchange, and condensation with triethyl orthoformate. Its silver, copper, cobalt, and nickel complexes [Ag2(L)2(CH3CN)2](PF6)2 (1), [CuL(CH3CN)2](PF6) (2), [CuL(phen)](PF6) (3), [CuL(dppe)](PF6) (4), [Co(L)2(CH3CN)2](PF6)2 (5), and [Ni(L)3](PF6)2 (6) have been synthesized and fully characterized by NMR, elemental analysis, and X-ray diffraction analysis. The copper complex 2 exhibits excellent catalytic activity in the Cu(I)-catalyzed azide–alkyne cycloaddition reaction of 2,2,6,6-tetramethylpiperidinyl-1-oxy-tethered alkynes in an air atmosphere at 50 °C.